Sky Dayton, the founder and CEO of Helio, is stepping down as the top executive of the hip cell phone company.

The company sent out a press release late Monday saying that Dayton, who also founded the Internet service provider EarthLink and Wi-Fi hotspot provider Boingo, would relinquish his CEO position. Wonhee Sull, formerly Helio's president and chief operating officer, will take over as CEO. And Dayton will become chairman of the company, replacing Jinwoo So, president of global business at SK Telecom.

Helio has been downplaying Dayton's departure. Brook Hammerling, Helio's spokeswoman said in an e-mail that Dayton's departure should not come as surprise, since he "loves to start things, build teams and brands and then pass the reigns onto a more day to day ops person."

The company pointed out that Dayton typically leaves his start-ups after three years. He supposedly followed similar timelines with EarthLink and Boingo Wireless. Now three years into the Helio venture, Dayton is handing the day-to-day operational reins over to someone else.

"Helio has reached a point in its development where I feel the timing is right for this change," Dayton said in a statement.

Because Helio is a privately held joint venture, it's been difficult to tell how well it's been performing financially. For the most part, the company has kept quiet about subscriber numbers and other details of its performance.

In what appears to be an effort to deflect any speculation that Dayton is leaving because the company is in trouble, Helio has decided to share some information about its business. In today's press release it claimed that the company now has more than 200,000 subscribers. And while this is tiny compared with the millions of customers who subscribe to Verizon Wireless or AT&T, the company claims to have some of the highest average revenue per user (ARPU) in the industry, with users spending more than $85 a month. The company said it closed its first full year of operation, which was 2007, with a revenue run rate of more than $240 million based on financial figures available in December.

The company also claims its subscribers are "voracious users of its data services." For example, users send on average more than 550 text messages per month. And roughly 95 percent of Helio subscribers access the Web from their mobile phones. The company also claims that it is seeing strong uptake in customized services for its users. For instance, 60 percent of Helio customers access MySpace via their Helio phone each month. And Helio claims that 57 percent of subscribers who had the Ocean handset downloaded Helio's exclusive YouTube application within two weeks of the launch.

More detailed financial information could become available when EarthLink reports its fourth-quarter earnings on February 7.